Most time, when I would make $$$ on the short shares, my broker called me to request immediate close. had to exit right before big gain.
Hence, I agree what CM Laoda said.
My broker is scottrade.
1. not easy to borrow shares. TZA, FAZ, even ERY.
2. couldn't hold short position long. Often, once market moved to the direction you expected, broker started to call you to request to close. Your good plan would be ruined by this request.